Contaminated or failed air flow sensor element; Damaged, corroded or loose sensor connector or terminals; Wiring fault such as open circuit, short to earth or short to supply between sensor and control unit; Unmetered air entering after the sensor from a split intake hose or loose clamp, or a blocked air filter or intake restriction; Missing or low sensor supply voltage or poor earth, such as a relay or fuse fault (depends on model); Fault inside the engine control unit.

P0100

Mass or Volume Air Flow Sensor A Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
00: FaultThe specific fault in that area

What it means

P0100 is the generic code for a fault in the Mass or Volume Air Flow Sensor 'A' circuit. The engine control unit has detected a signal from the air flow sensor that is missing, out of range or electrically implausible. This is a circuit-level fault, so wiring, connectors, the supply or the sensor itself may be involved, and the exact signal type depends on the sensor fitted to the engine.

Symptoms

Malfunction indicator lamp on
Poor or hesitant acceleration
Rough or unstable idle
Engine stalling or difficult starting
Poor fuel economy
Car running in a reduced-power or limp mode

Possible causes

Contaminated or failed air flow sensor elementlikely
Damaged, corroded or loose sensor connector or terminalslikely
Wiring fault such as open circuit, short to earth or short to supply between sensor and control unitlikely
Unmetered air entering after the sensor from a split intake hose or loose clamp, or a blocked air filter or intake restrictionpossible
Missing or low sensor supply voltage or poor earth, such as a relay or fuse fault (depends on model)possible
Fault inside the engine control unitrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine load, speed and coolant temperature, then check for other related codes.
Visually inspect the air filter, intake pipework between the sensor and throttle body, clamps and the sensor housing for damage, leaks or contamination.
Inspect the sensor connector and wiring for corrosion, bent or pushed-back pins, chafing and heat damage, and check the connection is secure.
With the ignition on and then at idle, view live air flow data and compare it with the expected value for the engine; check it responds smoothly to throttle opening and does not read zero or a fixed value.
Check the sensor supply, earth and signal circuits with a multimeter against the manufacturer's wiring diagram, including any fuse or relay feeding the sensor.
Carry out wiggle tests on the harness while watching live data for dropouts.
Check for intake air leaks, for example with a smoke test, as these can cause implausible readings and similar symptoms.
If the circuits and supply are proven good, test the sensor against the manufacturer's specification or compare it with a known good unit before replacing it.

How to fix

Repair or replace damaged wiring, terminals or the connector, and restore proper insulation and routing.
Fix any supply, earth, fuse or relay fault found in the sensor circuit.
Replace the air flow sensor if it is proven faulty or if cleaning with an approved sensor-safe method does not restore correct readings.
Repair or replace split intake hoses, loose clamps or leaking gaskets, and fit a new air filter if it is blocked.
Check for an updated control unit software calibration only if the manufacturer lists one for this fault; otherwise suspect the control unit last.

Can I keep driving?

Medium severity

The car can usually be driven short distances, but expect poor performance and possible stalling or limp mode, so get it fixed soon. Avoid long journeys or heavy loads, and stop if the engine stalls repeatedly or loses power in traffic.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.